Orkney Islands (Norse, Orkneyar, from ork, whale, and eyar, islands; Lat. Orcades), a compact group lying off the N. coast of Scotland, separated from it by Pentland frith, between lat, 58° 44' and 59° 23' N., and lon. 2° 24' and 3° 26' W.; area, about 5C0 sq. m., of which about one fourth is under cultivation; pop. in 1871, 31,274. The group includes 67 islands, of which 29 are inhabited. The principal are Pomona or Mainland, Hoy, North and South Ronaldshay, Westray, Sanday, Eday, Stronsay, Rousay, and Shapinsay. Many of the uninhabited islands are small holms used for pasturage, and others are rocky islets devoid of herbage. Sanday is the most fertile. Hoy alone of the group can be called mountainous, its greatest elevation being 1,600 ft, Geologically the islands belong to the old red sandstone formation, though granite is found near Stromness in Pomona. In the peat mosses which abound throughout the group traces of ancient forests have been discovered, but the climate is now unfavorable to the growth of trees. The soil is chiefly clay and sand, intermixed with peat mosses, and shell marl and bog iron ore are met with. There are no large streams, but springs of pure water abound, and there are several lakes, the largest of which is Stennis, in Pomona, 14 m. in circuit.

There is but little frost or snow; the range of the thermometer is from 25° to 75°, and the mean annual temperature is 45°. Until recently agriculture has been neglected, and the manufacture of kelp, the fisheries, and pasturage have been prominent. Much less kelp is produced than formerly, and more land has been brought under cultivation. The small native breeds of cattle, sheep, and ponies have been improved by the introduction of new stock. Rabbits and poultry are numerous, game abounds, and in the season of incubation the cliffs swarm with sea fowl. The cod and herring fisheries are very productive, and large numbers of lobsters are exported. The leading manufacture, employing about 2,000 girls, is straw plait for bonnets; some linen and woollen goods are made; and boat building and sail and cordage making are among the industries. The value of the exports, the chief of which are fish and cattle, is about £200,000 a year. The Orkneys, with Shetland, form a county returning one member to parliament. - Pomona, or Mainland, the principal island, is 24 m. long, with a breadth of from 3 to 15 m.; area, about 150 sq. m. The coast is broken up with bold cliffs, but has several good harbors. The surface is moor and moss, with much good pasturage, and a few fertile valleys.

On the shore of Lake Stennis, between Kirkwall and Stromness, is a remarkable group of 70 or 80 large symmetrical standing stones, in two separate circles of 100 ft. and 360 ft. diameter, the largest stones in the smaller circle. There are several smaller lakes. Kirkwall, the capital (pop. in 1871, 3,434), is a very ancient place, but has many new and handsome shops and houses. The principal building is the cathedral of St. Magnus, founded in 1138; it is a superb structure of red sandstone in the mixed Gothic and Saxon style, and the choir is used as a parish church. There are also a Presbyterian church, a grammar and other schools, town hall, two libraries, and several charities. Adjoining the cathedral are the ruins of the bishop's and the earl's palaces, and the museum contains numerous ancient relics. The most remarkable discovery, made in 1858, consisted of massive pins, brooches, bracelets, and other ornaments, and silver coins which are believed to have been contemporaneous with the earliest kings in Scottish or Scandinavian history. Kirkwall has a good harbor and a considerable export trade. Stromness, on the S. W. side of the island, 12 m. from Kirkwall (pop. 1,619), is important for its fisheries, and has a convenient and commodious harbor.

The red sandstone in the vicinity abounds in rare fossils. - The same Celtic people who colonized S. and N. Britain were the original inhabitants of the Orkneys. The islands were visited by Agricola, A. D. 84, and were afterward favorite resorts of the piratical Northmen. In 876 Harald Harfager subdued both the Orkneys and the Hebrides. On his return to Norway he conferred the administration of his conquest on Ronald, the father of Rollo, the ancestor of William the Conqueror.

In 920 Sigurd, the brother of Ronald, received this dominion from him, and afterward added to it considerable territory on the mainland of Scotland; and the two brothers thus became the founders of a long line of Scandinavian earls who affected the style of independent princes. In 1098 they became subject to the Norwegian crown. When James III. of Scotland married Margaret of Denmark (1469), he obtained the Orkney and Shetland islands as security for her dowry; and as they were never ransomed, they have ever since appertained to Scotland.